Executive Dysfunction in Children and adolescents with Attention Deficit Hyperactivity Disorder (ADHD) Original Article

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1 Original Article Executive Dysfunction in Children and adolescents with Attention Deficit Hyeractivity Disorder (ADHD) 1, 2, 3 Mehdi Tehrani-Doost, MD Reza Rad Goodarzi, MD 2 Mitra Seasi, MS 1 Javad Alaghband-Rad, MD 1, 2 1 Deartment of Psychiatry, Roozbeh Psychiatry Hosital, Tehran University of Medical Sciences, Tehran, Iran 2 Institute for Cognitive Science Studies (ICSS), Tehran, Iran 3 Psychiatry & Psychology Research Center, Tehran University of Medical Sciences, Tehran, Iran Corresonding Author: Mehdi Tehrani-Doost, M.D Associate Professor of Child and adolescent Psychiatry, Roozbeh Psychiatry Hosial, South Kargar Avenue Tehran, 13185, Iran tehranid@tums.ac.ir Tel: Fax: Objective: The urose of this study is to comare the executive functions in children and adolescents who suffer from attention deficit hyeractivity disorder (ADHD) with normal children. Method: Twenty children with ADHD were comared to 19 healthy children in terms of some executive functions using the comuterized version of Tower of London, Continuous Performance Test (CPT), and Stroo Color Test. Results: In Tower of London, the erformance of children with ADHD was worse than normal children (<0.05). In Continuous Performance Test, the commission errors in children with ADHD were significantly more than the normal grou (<0.01). In Stroo Test, the time sent to name the colors was significantly higher in ADHD grou. A significant correlation was also found between the erformance of children on Tower of London and CPT (P<0.05). Conclusions: This study demonstrates that children and adolescents who suffer from ADHD have some imairment of executive functions, articularly lanning and inhibition to resonse, but not in attention. Keywords: Attention deficit disorder with hyeractivity, attention, inhibition, Neurosychology Iran J Psychiatry 2007; 2: Individuals with attention deficit hyeractivity disorder (ADHD) are characterized by having hyeractivity, imulsivity, and inattention. Executive dysfunction is one of the cognitive deficits which have been suggested in ADHD. Executive function is the ability to maintain an aroriate roblem solving set to attain future goals. Anexecutive function (EF) deficit theory of ADHD, has been roosed by several researchers (1). Executive functions include set shifting and set maintenance, interference control, inhibition, integration across sace and time, lanning and working memory (2). In neurosychology, executive functions are described as the erformance on thasks that atients with frontal lobe lesions do badly on. Persons with ADHD have been found to exhibit deficits in most of EF abilities. In his review on executive functions in children with ADHD, Pennington found that 15 out of 18 studies have established a significant difference between ADHD atients and controls on one or more executive functions measures. He then concluded that the most consistently imaired measures are Tower of Hanoi, Matching Familiar Figure Test, Stroo Test, and measures of inhibition (2). The main cognitive model linking executive deficit to the behavioral symtoms of ADHD is that three cardinal symtoms of ADHD (hyeractivity, inattention and imulsivity) can be reduced to deficit in inhibition which is one of the executive functions (2-4). Moreover, it has been roosed that these children have some imairment in frontal lobe functions(5). In his review on studies of frontal lobe functions in children with ADHD, Barkley found that most of these tests assess the ability of resonse inhibition. It is believed that these tests are mediated by the frontal lobes; articularly, the orbital refrontal and medialrefrontal areas and their rich connections to the striatum (6). Wisconsin Card Sorting test, Stroo Test, Matching Familiar Figures Test, Tower of Hanoi, and Tower of London are several neurosychological tests used to assess executive functions. Planning and organizing are the two executive functions believed to be imaired in children with ADHD. Tower of London is one of the neurosychological tests which measures lanning. The main aim of this study is to find whether children and adolescents with ADHD are imaired in lanning, inhibition, set-shifting, and attention comared to the normal grou and to find the correlation between the variables of Tower of London task and those of Continuous Performance Test and Stroo Test. 25

2 Tehrani-Doost, Goodarzi, Alaghband-Rad Materials and Method Particiants: A total number of twenty boys aged 7 to 15 were recruited for this study. ADHD was diagnosed according to DSM-IV-TR classification by a child and adolescent sychiatrist (author) at a child sychiatry clinic. They did not have any other sychiatric or medical roblems excet for oositional defiant disorder. Their IQs were above 90. Nineteen children from the mainstream schools whose IQs and ages matched with their counterarts were examined as the control grou. Based on interviews with their arents and using the Conners' Parent Rating Scale, the control grou did not have any sychiatric roblems. Measures All of the articiants were examined using the measures below : 1) Conner s Parent Rating Scale 48 (CPRS-48): a 48- item questionnaire which was comleted by arents. Five indices have been derived from this scale: conduct roblem, learning roblem, hyeractivity imulsivity roblem, sychosomatic-anxiety roblem, and hyeractivity index. This questionnaire was used to comare the symtoms of hyeractivity, imulsivity, and inattentiveness between the two grous. 2) Raven Progressive Matrices: The Color Raven Progressive Matrices tye was used to measure the subjects intellectual abilities. 3) Comuterized Version of Tower of London: Tower of London was originally designed by Shallice (1982) to investigate lanning abilities in atients who suffer from frontal lobe damage. In this test, articiants are required to move an array of colored beads mounted on three vertical rods to match a articular goal arrangement(7). Robin Morris (1993) roduced a comuterized version of this task in which the beads are shown as discs to reresent three dimensional structures (8). The subjects are shown two arrangements on a touch sensitive screen. The to one remains static for each trial and reresents the goal arrangement. The bottom one contains the discs that can be arranged by the articiant to match the to arrangement. Discs can be moved by touching the disc first and then touching the required destination. The goal osition for the discs is varied, but the starting osition is ket static. The roblems can be solved in two, three, four and five moves(9). The variables are as listed: 1) number of moves, the mean number of moves above the minimum number ossible which is calculated as a general measure of erformance; 2) lanning time, is the time between the resentation of the roblem and touching the first disc; 3) subsequent thinking time, is the time between selection of the first disc and comletion of the roblem and can be used as a measure of erformance (8). Tower of London was used to evaluate lanning ability and is suosed to be sensitive to frontal lobe (7, 8, 10, 11). (4 Continuous Performance Test (CPT) was used to measure imulsivity and attention. There are several versions of CPT. The main rocedure is that a target stimulus is resented on the screen randomly among different stimuli. The articiant is instructed to ta a button when the target is resented. In this version, the articiant is shown some atterns containing a number and a figure. When two identical atterns (number and figure) are resented, the articiant should ta a button. The variables are as follows: 1) the number of Commissions which is the index of imulsivity. The commission error will occur if the subject resonses to a stimulus other than the target; 2) the number of Omissions, indicating the inattentiveness. The omission error will occur when the subject misses the target; 3) The" Reaction Time, the time between the resentation of the target and the resonse of the articiant (12). (5 Stroo Color Test was used to measure attention, set shifting, and cognitive flexibility. Three cards are resented to the articiant. The first one is called Dots Cards with several dots in colors of green, red, blue and yellow and the subject is told to name the colors. The second card which is called Word Card has several common words rinted in the same colors of the Dots Card. The articiant is required to name the colors of the rinted words without reading them. The third card is called Color Card on which the words of green, red, blue, and yellow are rinted in the same colors of the Dots Card but in different color of its own. The subject is instructed to name the rinted colors regardless of the meaning of the words. The errors and the time to comlete reading in each card are recorded. The subtraction of time in Dots Card from the time in Color Card is used as a Difference Index. Procedure After articiants were interviewed by a child and adolescent sychiatrist and ermission was obtained from their arents, they were referred for additional assessments. Particiants were examined using the comuterized Tower of London, CPT, Stroo Test, and Raven. The order of the tests varied randomly to avoid the influence of the order effect. The articiants were allowed to have a rest between the two tests. Meanwhile, their arents were also asked to comlete the Conner s Parent Rating Scale. Analysis The data was analyzed using the SPSS T-test was used to find the significance of differences in variables between the two grous. Pearson Correlation Test was used to find the correlation between the variables in each of the two tests in ADHD grou. P value less than 0.05% was noted as significant. Results Demograhic characteristics of the articiants are demonstrated in Table 1. 26

3 Table 1. Demograhic Characteristics of articiants P IQ Age (months) Table 4. Characteristics of two grous in CPT P Commission errors Omission errors Reaction time Table 2. Characteristics of two grous in Conners Parent Rating Scale Control ADHD (N=20) (N=19) Conduct roblem Learning roblem Psychosomatic Hyeractivity imulsivity Hyeractivity index T-test revealed no significant difference between the ADHD and control children on their ages and IQs. The results of Conners Parent Rating Scale in two grous were shown in Table 2. A significant difference was found between the two grous in terms of hyeractivity indext t(37)=14.69; P<0.01. Excet for sychosomatic roblem, a significant difference was also observed between the two grous in other indices of CPRS. Conduct roblem was more revalent in hyeractive children than the control grou, t(37)=7.35; P<0.01. In the Tower of London Test, the number of moves was higher in children with ADHD than the normal grou. This difference was significant at level 2 and 3, t(36) = 2.15; P<0.05, t (37)=2.06; P<0.05. Subsequent thinking time was also significantly higher in ADHD grou comared to normal children. In terms of lanning time a significant difference was found at level 2, where the lanning time in ADHD grou was higher (P< 0.01). Table 3 shows the results of Tower of London Test in the two grous. In Continuous Performance Test (CPT), the number of commissions in atients who suffer from ADHD was significantly higher comared to the normal grou t(37)=3.11;p<0.01. Nevertheless, no significant difference was found between the two grous in Table 3: Result of Tower of London test in two grous Number of moves Level Level Level Level Sub Thinking time Level Level Level Level Planning time Level Level Level Level Table 5. Characteristics of two grous in Stroo Test Time in dots Card Errors in dots card Time in word card Errors in word card Time in color card Errors in color card omission errors. Reaction Time in the two grous was not significantly different. Table 4 shows the differences between two grous in terms of the variables of CPT. Time taken to name the colors in Dots Card, Word Cards, and Color Card were significantly higher in ADHD children than normal grou. [Dot: t(37)=2.59; P<0.05; Word: t(37)=2.03; P<0.05; Color: t(35)=2.32; P<0.05]. In terms of errors, the difference between the two grous was not significant. The Difference Index which is the subtraction of Dot time from Color time (C time D time) was higher in ADHD grou. This difference, however, was not significant.table 5 shows the difference between two grou in term of the variable of stroo test. Pearson Correlation test was used to find the correlation between different tasks. With resect to the correlation between Stroo Test and CPT, there was a correlation between commissions in CPT and the number of errors in Color Card, r=0.49; N=20; P<0.05. Concerning the relation between Tower of London Test and CPT, there was a significant correlation between the number of moves at levels 3, 4 and 5 in Tower of London and the number of omissions in CPT (level 3: r=0.45; N=20; P<0.05, level 4: r=0.53; N=20; P<0.05, level 5: r= 0.53; N=20; P<0.05). Regarding the correlation between hyeractivity index in Parent Conner s Rating Scale and CPT, there was a significant correlation between this index and commissions in CPT, r=0.63; N=20; P<0.01. Table 6 reresents the correlations between Tower of London Test and the other neurosychological measures used in this study. Difference Index (C time D time) in Stroo Test showed a significant correlation with omissions in CPT, r=0.44; N=20; P<0.05. Discussion The executive dysfunction hyothesis in attention deficit hyeractivity disorder has been roosed in several studies. It has been found that children and adolescents who suffer from ADHD have imairment in resonse inhibition and this leads to hyeractivity, imulsivity and inattention. It has been suggested that these atients have deficit in other tyes of executive 27

4 Tehrani-Doost, Goodarzi, Alaghband-Rad Table 6. Correlation between Tower of London Test and Stroo Test and CPT Stroo Test Continuous Performance Test (CPT) Time Error Difference score Commissions Omissions Tower of London Test Number of moves Level Level * Level * ** * Level * Subsequent Thinking time Level Level Level Level Planning time Level Level Level Level Notes: ** P< 0.01, * P<0.05, P<0.06Discussion functions such as lanning. To find any deficits of lanning, attention and set shifting in atients with ADHD comared to normal children we conducted this study. This study shows that comared to normal children, children with ADHD erform oorly on Tower of London Test, which assesses lanning, and roblem solving. This result is consistent with findings in Pennington s review (2). Culbertson and Zilmer comared children with ADHD to normal grou using manual tye of Tower of London. They found that ADHD grou erformed oorly on this task (13). In Kemton s study, children with ADHD were examined by comuterized version of Tower of London. It was found that before treatment, these children had a oor erformance on this task comared to the normal grou and the ADHD grou who took medication. These findings suort the hyothesis that ADHD children have imairment in executive functions including lanning (2-4). This study also indicates that comared to normal children, the ADHD grou had imairment in imulsivity index on Continuous Performance Test (CPT). This difference was not significant in attention index of this test. This finding is suortive of the theory that states imairment in resonse inhibition is the main deficit of ADHD. One ossibility is that ADHD children have imulsive resonses; therefore, their commissions in CPT will increase, and their omissions will decrease by chance. Another test used in this study was Stroo Test which assesses a number of cognitive functions including attention, resonse inhibition, and set shifting. According to Pennington s review, Stroo Test is one of the tasks found to be imaired in children and adolescents with ADHD(2). In this study, no significant difference was found on number of errors between the two grous. It was, however, discovered that the time sent to name the colors in all cards was significantly higher in children and adolescents with ADHD. Since children with ADHD are distractible, it takes more time for them to comlete a task, esecially when they need to shift from one category to another. This study also found that there is a significant correlation between Tower of London test and CPT in children with ADHD. It means that the lanning erformance of these children is related to their imulsivity. This finding is consistent with the results found in the Anderson s study which showed a significant correlation between Tower of London and other measurements of executive functions(14). Since the tests used in this study are sensitive to frontal lobe (8, 10, 11), this study can suort the frontal lobe theory of ADHD (6). This hyothesis has been suggested in several studies (15, 16). According to these findings, ADHD children have imairment in executive functions due to frontal dysfunction (2). This theory has also been confirmed by some functional neuroimaging studies. Namely, Rubia s study which found a lower ower of resonse in the right mesial refrontal cortex during the motor resonse inhibition tasks in children with ADHD using fmri (17). In her study, Smith found a decreased activation in the left rostral mesial frontal cortex during erformance of tasks that assessed motor resonse inhibition using fmri in adolescents with ADHD (18). In his study on children with ADHD, Pliszka also found that articiants failed to activate the anterior cingulat cortex and the left ventrolateral refrontal after unsuccessful inhibition during the sto task using fmri (19). In Summary, this study found that ADHD children have imairment in executive functions including resonse inhibition and lanning. One of the limitations of this study may be the high level of the articiants IQs which could influence their erformance of executive functions tasks even though the two grous were matched on their IQs. 28

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